Concern with air pollution caused by engine exhaust emissions has risen dramatically in recent years. Accordingly, intensive efforts have been made to design engines which burn clean. However, engines which have been designed to burn clean tend to become dirty with increased use. In addition, there are millions of automotive vehicles on the road which were designed before concern with air pollution developed. Accordingly, there is a need for a device which is compatible with all automotive vehicles and which minimizes air pollution from engine exhaust.
Heretofore, efforts have been made to give the motor vehicle muffler the additional function of cleaning or filtering the engine exhaust. Such prior devices have the effect of increasing engine back pressure, as exemplified by the patent to Bembinster, U.S. Pat. No. 3,115,209. However, an increase in engine back pressure decreases engine efficiency and this, in days of high fuel cost, is objectionable. To overcome this problem, as exemplified by the patent to Kile, U.S. Pat. No. 3,593,499, a motor-driven fan was put inside the muffler. Such devices, however, necessarily reduce engine efficiency by the amount of energy necessary to drive the fan, and, in addition, such devices are expensive and liable to failure caused by heat and vibration.
These problems have now been overcome, as shown herein, by providing a combined muffler and filter which has no moving parts and which is formed from a fixed outer shell and an inner shell. The inner shell comprises concentric perforated tubes, the space between these tubes is filled with a filtering material and this material is kept in position by layers of fiberglass wrapped around the outer surface of each tube. The fiberglass has the added function of serving as an auxiliary filter to trap particles of engine exhaust which are not stopped by the filtering material. The length of the concentric tubes, their size, as well as the comparatively small radial distance the exhaust gasses must travel through the concentric tubes, is selected to adequately filter the engine exhaust without producing an objectionable increase in back pressure. The spacing between the inner and outer shell provides the volume necessary to muffle the engine noise.
An important object of this invention, therefore, is to provide a combined motor vehicle muffler and engine exhaust filter which filters the engine exhaust without substantially increasing engine back pressure.
A further object of this invention is to provide a combined muffler and engine exhaust filter which has no moving parts and which provides a filtering action without an objectionable increase in engine back pressure .